Without a doubt, fiber optic technology will become the main means of information transmission in the future. It is one of the reasons for the massive growth of international telecommunications and the "shrinking of the planet" effect. Based on this technology, the Internet was able to become the invaluable information tool that it is today. However, contrary to popular belief, this is not a panacea. Fiber optic systems still have many limitations and hurdles to overcome. Before we start discussing the theory of fiber optic transmission, let's compare traditional and fiber optic cables and evaluate their advantages and disadvantages.
1.2.1. Bandwidth
Optical fiber
Today, fiber optic cables have huge bandwidth, with transmission rates up to 40 Gb/s in place today and over 100 Gb/s in the near future. At present, the factors limiting the growth of transmission rates are: firstly, the response time of sources and detectors for high data transmission rates is large compared to the pulse periods; secondly, the proximity of the wavelength of light to the period of the pulse, causing differentiation problems in detectors. Techniques for multiplexing multiple wavelengths on a single fiber (called wave division multiplexing (WDM) increase the overall transmission rate over a single fiber to several Tbit/s.
The following comparison will give you a sense of what this means in terms of information transfer: with fiber optic communication at a speed of approximately 1 Gb / s, more than 30,000 compressed telephone conversations can be transmitted simultaneously. With a 30Gbps connection, up to 1 million telephone conversations can be transmitted simultaneously over a single glass fiber!
Cables
Coaxial cables up to 8 cm in diameter can provide transmission rates up to 1 Gbps over distances up to 10 km. The limiting factor is the very high cost of copper.
Important research is currently ongoing to increase transmission speed over twisted-pair cables. Today, 100 Mbps speeds are quite common in many local area networks. Commercial systems are also available, operating at speeds up to 1 Gbps. After successful laboratory tests at 10 Gb/s speeds, the corresponding products are being prepared for commercial release. The reason for this activity in this area lies in the abundance of infrastructure with already installed twisted-pair cables, which can significantly save on digging trenches, laying channels and laying new fiber optic cables. For this reason, twisted-pair cable technology currently competes successfully with fiber optic technology, since both have many common applications.
1.2.2. Interference
Optical fiber
Fiber optic cables are completely immune to electromagnetic interference (EMI), radio frequency interference (RFI), lightning and high voltage surges. They do not suffer from capacitive or inductive coupling problems. When properly designed, fiber optic cables should not be affected by electromagnetic pulses from nuclear explosions and background radiation. (This news will console a large part of the population after a nuclear war!)
In addition to this fact, fiber optic cables do not create any electromagnetic or radio frequency interference. This property is very valuable in computing, video and audio processing, where a low noise environment is becoming increasingly important for improved playback and recording quality.
Cables
Ordinary cables are affected by external interference. Depending on the types of cables and their degree of shielding, they are subject to varying degrees of electromagnetic and radio interference through inductive, capacitive and resistive coupling. Communication systems based on traditional cables completely fail under the influence of electromagnetic pulses from nuclear explosions.
Ordinary cables also radiate electromagnetic waves, which can cause interference in other cable communication systems. The amount of radiation depends on the magnitude of the transmitted signal and the quality of the screen.
1.2.5. electrical insulation
Optical fiber
Fiber optic cables provide complete galvanic isolation between both ends of the cable. The non-conductivity of the fibers makes the cables insensitive to voltage surges. This eliminates EMI and EMI that can be caused by ground loops, common mode voltages, and ground potential offsets and shorts. The fiber optic cable acts as a long insulator. Since optical fibers do not radiate waves and are not subject to interference, another advantage is the absence of mutual influence of cables (that is, the effect of the radiation of one communication cable on another laid next to it).
Cables
Traditional cables, simply by working as intended, provide an electrical connection between their ends. Therefore, they are susceptible to electromagnetic and ether interference from ground loops, common mode voltages, and ground potential offsets. They are also subject to problems of mutual influence.
1.2.4. Transmission distances
Optical fiber
For simple, low-cost fiber optic systems, repeater distances of up to 5 km are possible. For high-quality commercial systems, repeater distances of up to 300 km are now easily available. Systems (without the use of repeaters) for distances up to 400 km have been developed. Distances close to 1000 km have been achieved in the laboratory, but are not yet available on the market. One European the company said it is currently developing a fiber optic cable that can run along the earth's equator and, without any repeaters, be able to transmit a signal from one end to the other! electrons in the shell, which in turn emit photons with higher energy.Thus some form of auto-amplification occurs.The following chapters will explain the terms used to the reader.
Cables
In the 4 Mbps twisted-pair cabling market, repeater distances of up to 2.4 km are available. In the case of coaxial cables at speeds less than 1 Mbit/s, distances of up to 25 km between repeaters are possible.
1.2.5. Size and weight
Optical fiber
Compared to all other data transmission cables, fiber optic cables are very small in diameter and extremely light. A 4-core fiber optic cable weighs approximately 240 kg/km, while a 36-core fiber optic cable only weighs approximately 3 kg more. Because of their small size compared to traditional cables of the same bandwidth, they are usually easier to install in existing environments, and installation time and cost are generally lower because they are light and easier to work with.
Cables
Traditional cable can weigh from 800kg/km for 36 twisted pair cable to 5t/km for high quality large diameter coaxial cable.
To date, optical cable has become widespread in the creation of telecommunication networks. Its characteristic features include such indicators as:
- high data transfer rate;
- lack of susceptibility to various interferences;
- compared to copper cables, low weight and overall dimensions;
- high duration of service life;
- the possibility of increasing the distance between the transmitting devices up to 800 km.
Perhaps the only drawbacks that can be identified when creating a network of fiber optics are the high cost of materials and equipment, the labor-intensive process of cable installation, associated with the need for welding when laying the main highways.
Optical cable design
- 1 - central power element
- 2 - optical fibers
- 3 - plastic tube modules
- 4 - film
- 5 - thin inner shell made of polyethylene
- 6 - Kevlar threads or armor
- 7 - outer thick polyethylene sheath
Fiber bandwidth
Over the past few decades, the bandwidth of fiber optic cable has increased significantly. At the same time, developments to improve one of the advanced data transmission technologies do not stop even for a minute. In essence, the signal transmission speed largely depends on the distance between the equipment, the type of fiber carrier and the number of connecting joints in the trunks.
For example, a multimode optical cable used in building an internal network (between data servers) at a distance of approximately 200 meters is capable of providing speeds of up to 10 Gb / s.
For laying external communications, where the distance between transmitters can reach several tens of kilometers, single-mode fiber is used. The structure of such a cable allows you to develop a flow rate of more than 10 Gb / s. True, this is far from the limit of the possibility of optics. With an increase in consumer demand, there will be a need to increase the capacity of equipment, and even the replacement of equipment that allows achieving a data transfer rate of 160 Gb / s is not able to fully use the potential of the carrier.
Types of fiber optic cable
According to its structure, fiber optic cable is divided into two categories:
- multimode;
- single-mode.
Multimode optical cable has proven itself as a conductor that transmits a signal over short distances. First of all, this is due to the structure of the fiber itself, in the name of which the word “a lot” means far from what is considered to be a good indicator. The recommended distance, when laying a multimode cable, from the transmitting device to the user should be no more than one kilometer. At this distance, the conductor shows excellent ability to transmit the light flux with virtually no loss and is capable of providing speeds up to 10 Gb / s. Thus, it can be used to build a network in a small area or as an optical cable for indoor installation.
A single-mode optical cable is primarily intended for data transmission over long distances, which can be in the tens or even hundreds of kilometers. In terms of its structure, this type of fiber has better qualities and is able to maintain a constant high data flow rate with virtually no attenuation in the optical cable. Thus, the throughput of a single-mode optical carrier is limited directly by the transmitting devices and, with powerful equipment installed, can reach several Tbps.
Necessary equipment for transmitting information over fiber optic cable
To date, fiber optic networks have become widespread among companies that provide their subscribers with access to the Internet. At the same time, for the implementation of data transmission, except for intermediate couplings and other related equipment, the following technique is used:
on the part of the provider: - special DLC equipment, also known as a multiplexer. It allows the transmission of data over a fiber-optic cable over long distances at a constantly maintained high speed.
on the part of the subscriber: - ONT router, which is the terminal client equipment and allows you to provide access to the Internet through a fiber optic network. Allows access at speeds up to 2.5 Gbps.
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26 terabits/s over fiber with a single laser
A team of German engineers led by Prof. Wolfgang Freude from the University of Karlsruhe has applied OFDM (Orthogonal Frequency Division Multiplexing) technology, which is widely used in wireless communications (802.11 and LTE), digital television (DVB-T) and ADSL, to optical fiber. .
It is more difficult to use OFDM in optical fiber, because here you need to divide the light flux into subcarriers. Previously, the only way to do this was to use a separate laser for each subcarrier. Comparison of different types of multiplexing
A separate laser and a separate receiver are used for broadcasting on each frequency, so that hundreds of lasers can simultaneously transmit a signal on a single fiber optic channel. According to Professor Freude, the total bandwidth of the channel is limited only by the number of lasers. "An experiment has already been carried out and a speed of 100 terabits / s has been demonstrated," he said in an interview with the BBC. But for this, about 500 lasers had to be used, which in itself is very expensive.
Freude and colleagues have developed a technology for transmitting more than 300 subcarriers of different colors over an optical fiber with a single laser that operates in short pulses. This is where an interesting phenomenon called optical frequency comb comes into play. Each small pulse is "smeared" in frequency and time, so that the signal receiver, with good timing, can theoretically process each frequency separately.
After several years of work, German researchers still managed to find the right timing, select the right materials and put into practice the processing of each subcarrier using the Fast Fourier Transform (FFT). The Fourier transform is an operation that associates a function of a real variable with another function of a real variable. This new function describes the coefficients in the decomposition of the original function into elementary components - harmonic oscillations with different frequencies.
The FFT is ideal for splitting light into subcarriers. It turned out that about 350 colors (frequencies) can be extracted from a normal pulse in total, and each of them is used as a separate subcarrier, as in the traditional OFDM technique. Last year, Freude and his colleagues conducted an experiment and in practice showed a speed of 10.8 terabits / s, and now they have further improved the accuracy of frequency recognition.
According to Freude, the timing and FFT technology he developed could well be implemented in a microcircuit and find commercial application.
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Optical fiber
1. What do the terms “terminating” a cable system and “splicing” a fiber optic cable mean? Termination - the procedure for connecting a cable, wire or fiber to switching equipment. Splicing - mechanical splicing of the ends of the fibers with each other using a clamp-clamp (splice). 2. Explain the concepts of "basic parameters" of the cable system and
"attenuation of fiber optic cable"? Attenuation is the process of attenuation of the light flux in an optical fiber. Factors causing attenuation can be different: - attenuation caused by the absorption of light. Defined as the conversion of a light pulse into heat associated with resonance in the fiber material. There are internal absorptions (related to the fiber material) and external absorptions (the presence of trace impurities). Optical fibers currently produced have a very small amount of microimpurities, so external absorption can be neglected. - attenuation of light in the optical fiber, caused by the scattering of radiation. Scattering is one of the main factors in the attenuation of light in a fiber. This type of attenuation is primarily associated with the presence of impurities in the optical fiber, as well as defects in the core of the optical fiber. The presence of such inclusions leads to the fact that the light flux, propagating along the optical fiber, deviates from the correct trajectory, as a result of which the angle of refraction is exceeded and part of the light flux exits through the sheath. Also, the presence of impurities leads to a partial reflection of the light flux in the opposite direction, the so-called backscatter effect; - light attenuation associated with bending of optical fiber, there are two types of bends: 1. Micro bending, this kind of bending is caused by microscopic changes in the geometrical parameters of the fiber core as a result of production. 2. Macrobending, the view is caused by a large bend in the optical fiber, which exceeds the minimum radius, while part of the light escapes from the core of the fiber. The bending radius at which the light pulse propagates without any distortion is 10 centimeters (for single-mode fibers). Increasing the minimum bend radius increases the scattering effect. The factors needed to determine the total attenuation factor are: optical input and output losses, absorption and scattering losses, bending losses, and mechanical connector losses. The attenuation coefficient is defined as the ratio of the power introduced into the optical fiber to the power received from the fiber of the optical signal. Measured in decibels (dB). 3. Describe the design and characteristics of a single-mode fiber optic cable. An optical fiber cable is a thin light-conducting glass or plastic core in a glass reflective sheath enclosed in a protective braid. Singlemode fiber - (singlemode) SM, 9-10 / 125 microns, that is, 9-10 micrometers is the core diameter, 125 microns is the cladding diameter. A light beam is transmitted with wavelengths of 1300 and 1550 nm and attenuation of 1 dB/km. 4. Describe the construction and characteristics of multimode fiber optic cable. multimode fiber - (multimode) MM, 62.5/125 and 50/125 µm: core diameter is 62.5 or 50 µm. A light beam is transmitted with wavelengths of 850 and 1300 nm and attenuation of 1.5-5 dB / km.
5. What fiber standards should be used
system administrator when organizing fiber optic
cable system? Currently, the following conformances to the IEC 60793 recommendation and the ITU-T recommendation (ITU-T) are defined, with the addition of the wavelength of a certain type of fiber:
Type B1.1 conform to ITU-T G652 (a, b) at 1.31 µm and ITU-T G654a at 1.55 µm;
Type B1.2 b complies with ITU-T G654 (b) with a wavelength of 1.55 µm;
Type B1.2 c complies with ITU-T G654 (c) with a wavelength of 1.55 µm;
Type B1.3 complies with ITU-T G652 (c, d) with a wavelength of 1.31 µm;
Type B2 complies with ITU-T G.653 (a, b) and ITU-T G.655 (a, b) with a wavelength of 1.55 µm;
Type B4 c complies with ITU-T G.655 (c) with a wavelength of 1.55 µm;
Type B4 d conforms to ITU-T G.655(d) at 1.55 µm wavelength;
Type B4 e conforms to ITU-T G.655(e) with a wavelength of 1.55 µm;
Type B5 complies with ITU-T G.656 with a wavelength of 1.55 µm;
Type B6 a complies with ITU-T G.657 A1/2 wavelength 1.31 µm;
Type B6 b complies with ITU-T G.657 B2/3 at 1.31 µm.
6. What cabling administration standards should
apply system administrator? The creation of cable systems is based on a set
standards. Here are the main standards required for
high-speed data transmission and mandatory
system administrator services.
EIA/TIA 568 - standard for the creation of telecommunications service
and industrial buildings, planning cable
building systems, methodology for building a telecommunications system
office and industrial buildings.
EIA/TIA 569 is a standard that describes the requirements for premises,
in which structured cabling is installed
communication system and equipment.
EIA/TIA 606 is a telecommunications administration standard.
infrastructure in office and industrial
EIA/TIA 607 is a standard that specifies requirements for
infrastructure telecommunications grounding system
and equalization of potentials in service and production
It is possible to use non-EIA/TIA standards, but standards
for building ISO structured cabling systems.
ISO 11801 - structured cabling standard
general purpose in buildings and campuses. It is functionally
similar to the EIA/TIA 568 standard. 7. What functions do cable management systems perform?
systems? Give an example implementation. Troubleshooting a network is a fairly complex process,
and the procedure for registering changes in the state of connections
manually is just as complicated and unreliable. Therefore, most often
and networks use cable management systems
systems to monitor system performance
and its individual components and troubleshoot as little as possible.
short time. 8. List the building cabling subsystems and their functions. 
workplace subsystem. The workplace subsystem is designed to connect end users (computers, terminals, printers, telephones, etc.) to an information outlet. Includes switching cables, adapters, as well as devices that allow you to connect terminal equipment to the network through an information outlet. The work of the SCS, in the end, ensures the work of the subsystem of the workplace.
horizontal subsystem. The horizontal subsystem covers the space between the Information socket at the workplace and the horizontal cross in the telecommunication closet. It consists of horizontal cables, information outlets and a part of the horizontal cross that serves the horizontal cable. Each floor of the building is recommended to be served by its own Horizontal Subsystem. All horizontal cables, regardless of the type of transmission medium, should not exceed 90 m in the area from the information outlet at the workplace to the horizontal cross. At least two horizontal cables must be laid for each workplace.
backbone subsystem. The trunk subsystem connects the main cross in the control room with intermediate crosses and with horizontal crosses. The backbone subsystem should include a cable installed vertically between the floor crosses in a multi-storey building, as well as a cable installed horizontally between the crosses in an extended building.
Equipment subsystem. The equipment subsystem consists of electronic communications equipment for collective (general) use, located in a control room or in a telecommunications cabinet, and the transmission medium necessary for connection to distribution equipment serving horizontal or backbone subsystems.
Highway of the complex of buildings. When the cable system spans more than one building, the components that provide communication between the buildings constitute the Campus Backbone. This subsystem includes the medium through which trunk signals are transmitted, appropriate switching equipment designed to terminate this type of medium, and electrical protection devices to suppress dangerous voltages when the medium is exposed to lightning and / or high voltage electricity, the peaks of which can penetrate the cable inside the building.
administrative subsystem. The administrative subsystem brings together the subsystems listed above. Consists of patch cords that physically connect different subsystems and labels to identify cables, patch panels, etc.
9. List the characteristics of the campus cabling system according to
TIA/EIA 568 standard. In accordance with the TIA/EIA 568 cabling system design standard, SCS has the following characteristics: topology of any subsystems - star; types of devices and rooms connecting cable subsystems: horizontal closet and cross (NS), intermediate closet and cross (1C), main closet and cross (MC) and control room (ER) - a room for active network equipment; the number of intermediate closets between the main and horizontal closet - no more than 1 closet; between any two horizontal closets - no more than 3 closets; maximum length of trunk segment for twisted pair - 90 m; does not depend on the type of cable; the maximum length of the trunk segment for fiber depends on the type of cable (see figure)
10. Give examples of cable system marking implementation according to the administration standard. GOST R53246-2008 Color code marking depending on the optical fiber class
11. What is a functional network diagram? When and how it
does the system administrator?
12. List the technical metrics of fiber optic cable
systems. How to correct them after deviations from
nominal values? Delays (Frame Delay Ratio). Latency is a critical parameter,
important for applications that work
in real time. This option has already been considered.
as a technical metric for 100 Base Ethernet.
The forum documents provide a theoretical calculation of this
parameter for Metro Ethernet. Quite problematic in practice.
complexity of modern systems).
Frame loss FLR (Frame Loss Ratio). Frame Loss
This is the proportion of frames not delivered to the recipient, from
total number of transmitted frames for the reporting period (hour,
day, month).
The impact of packet loss on user traffic, as well as
delays are different and depend on the type of data being transmitted.
Accordingly, losses can affect the quality in different ways.
QoS services depending on applications, services
or high-level telecommunication protocols,
used to exchange information. For example, losses
not exceeding 1% are acceptable for applications such as Voice
over IP (VoIP), however, increasing them to 3% makes it impossible
providing this service.
On the other hand, modern applications respond flexibly
to the growth of losses, compensating for it by reducing the speed
transmission or the use of adaptive compression mechanisms
Mathematical descriptions of FLR are also provided in the documents
FDV (Frame Delay Variations) is one
of the critical parameters for applications operating in the mode
real time.
FDV is defined as the delay difference between several selected
packets sent from one device to another. This metric only applies to successfully delivered
packets over a certain period of time. Her mathematical races
The couples are given in the forum documents.
Throughput dripped. Channel bandwidth
is the theoretical maximum of the possible transmitted
information and very often this concept in measurements
replaced by the concept of channel capacity,
which reflects the real possibility of the environment, i.e. the volume
data transmitted by the network or part of it in a unit of time.
Bandwidth is not a user specification,
since it characterizes the speed of execution
internal network operations - the transfer of data packets between
network nodes through various communication devices.
Percentage of channel bandwidth usage per unit
time is called channel utilization. Canal disposal
also often used as a metric. Bandwidth
measured either in bits per second or in packets
per second. Bandwidth can be instantaneous,
average and maximum.
Average throughput is calculated by dividing
the total amount of data transferred at the time of their transfer,
and a sufficiently long period of time is chosen
Hour, day or week.
Instantaneous throughput differs from average
throughput by choosing for averaging
a very small amount of time, such as 10 ms or 1 s.
The maximum throughput is the largest
instantaneous throughput fixed for
observation period.__
13. What business metrics does the system administrator use when
operation of the cable system? There are three main business metrics for IS performance.
Expected System Recovery Time MTTR (Mean
Time to Restore). This metric is set by business units
company system administrator services. There are types of business
which can survive without IP only a few
minutes, and then the price of downtime per minute will become critical
Other types of businesses may be waiting for system recovery
several days without financial losses. It's critical
metric for planning the recovery procedure. Price
on the application of preventive measures for recovery
system grows exponentially depending on the
MTTR values. System uptime is a metric that characterizes
system running time. This metric is similar to the metric
MTBF, discussed in Chapter 8, but takes into account not only
technical problems, and network maintenance problems. She is
used to measure network reliability and stability and
displays the time the network has been running without failure or need
reboot for administration or maintenance purposes.
System reliability is sometimes measured as a percentage (usually
not less than 99%). Too high a value may mean insufficient
system administrator qualifications
some processes require routine shutdown and reboot.
Expected time between failures MTBF (Mean Time Between
Failures), or MTBF, is a performance metric
equipment specified by the manufacturer. Since modern
computer hardware works fairly reliably
(very often the manufacturer gives a lifetime warranty),
then some manufacturers do not provide this metric in their technical
documentation. The system administrator should
in this case, take it from published analytical data
for this type of equipment.
System uptime Uptime is the resulting
a metric that tells how much time the user
does not use the IS due to error diagnostic problems and
system recovery, i.e. this is the total time for
search for errors, their diagnosis, recovery time and
launching the IC in industrial mode. This metric is set
business units to system administrator services in
SLA. It is determined based on financial capabilities.
enterprise and, accordingly, its equipment with means
diagnostics and recovery. For admin services
systems, this metric is reporting and determines their ability to
keep the IS in working condition. Service Availability provides a direct
impact on the actual quality of the service consumed
user. There are three most important criteria
determining the availability of the service: the time of implementation of the service
(Service Activation Time), connection availability (Connection
Availability), service recovery time after failure (Mean
Time to Restore Service - MTTR).
Service implementation time is the time that elapses from
the moment the user orders a new service (or modification of the parameters of an existing service) until the moment when
the service will be activated and available to the user. Time
installation can take from several minutes to several
months. For example, to modify an existing
service (at the request of the user) in order to increase
its performance may need a gasket
fiber optic cable to the user's location,
which will take a long time.
Connection availability determines how long the user
the connection matches the parameters of the contract.
Usually the value of this parameter is specified in the description of the service.
as a percentage (sometimes in minutes). Connection Availability
calculated as the percentage of time during which
the user connection was in a fully functional state
state (the user received and transmitted
data), from the total duration of the reporting period.
The service provider (for example, telecom operator) usually excludes
from downtime, the period of routine maintenance
works, because the user is about the upcoming prevention
notified in advance.
The service recovery time after a failure is defined as
expected time needed to restore normal
operation of the service after a failure. This metric is already
was discussed in Chapter 8. In addition, we note some of its
peculiarities. Most networks provide some
redundancy level with automatic recovery
services in the event of failures or malfunctions. For
in such situations, the telecom operator sets MTTR equal to
several seconds or even milliseconds. If a
intervention of technical personnel is required, this time
is usually taken equal to several minutes, less often -
14. What system administrator services should be
involved in the process of fiber optic restoration
cable system?
15. What is the work on the restoration of fiber optic cable
system and in which case the system administrator will give
outsourcing company?
16. Give an example of applying the basic model of finding errors
system administrator during "slow" operation of the fiber optic
cable system.
studfiles.net
Fiber optic cable - from selection to use
An optical fiber cable is not only a product that can be bought on the website of the Finfort-Intertrading company, it is, first of all, an integral component for building a reliable, trouble-free Internet network.
Fiber optics transmit data at a very high speed. With each new upgrade, not only the quality, but also the volume of transmitted information increases. The bandwidth of fiber optic cable is already measured in Tbps. But this is not the limit - there is an opportunity for a multiple increase in throughput.
How to choose fiber optic cable?
There are many specifications for fiber optics that cover different aspects such as dimensions, bandwidth, strength, bending radius, connector selection, and even the color of the sheath that protects the cable from damage.
Of the main parameters that you need to know, it is worth highlighting the length of the fiber, the diameter, the bandwidth of the fiber optic cable, the transparency window, and the signal attenuation.
If you order a cable on the Finfort-Intertrading website, always take it with a margin - suddenly you need to rearrange the equipment within the premises, additional meters or a whole coil will never hurt!
Optical connectors are required to connect the fiber optic cable to the equipment. The most popular are SC and ST connectors. All types of cable connectors are on the product page of the Finfort-Intertrading website - choose the right ones!
It is not difficult to choose and buy a fiber optic cable on the Finfort-Intertrading website. Here's what you may not know, so these are some of the nuances that rarely anyone pays attention to.
Never look directly into an optical fiber section. The optical energy that is transmitted through the cable is not visible to the eye, but it can permanently damage the retina.
Be careful when splicing the fibers. Fiber optic pieces are tiny, almost invisible, sharp pieces of glass that can damage the skin of the hands or get into the eyes. Use tape to pick up the pieces.
Make sure that the number of fibers in the cable of one network (outside and inside the building) matches as much as possible.
During fiber installation, test and document data such as the attenuation of each fiber. Make a description of the power of optical radiation during transmission and reception, indicate optical losses, patch panel location, connector type for each connection.
Of course, this is not all information about fiber optic cables. Detailed specifications are described on the Finfort-Intertrading website in the product section. Come in, choose, order!
The journal Nature Photonics published a description of a new technology for transmitting data over fiber at speeds up to 26 Tbps instead of the current maximum of 1.6 Tbps.
A team of German engineers led by Prof. Wolfgang Freude from the University of Karlsruhe has applied OFDM (Orthogonal Frequency Division Multiplexing) technology, which is widely used in wireless communications (802.11 and LTE), digital television (DVB-T) and ADSL, to optical fiber. .
It is more difficult to use OFDM in optical fiber, because here you need to divide the light flux into subcarriers. Previously, the only way to do this was to use a separate laser for each subcarrier.
Comparison of different types of multiplexing
A separate laser and a separate receiver are used for broadcasting on each frequency, so that hundreds of lasers can simultaneously transmit a signal on a single fiber optic channel. According to Professor Freude, the total bandwidth of the channel is limited only by the number of lasers. "An experiment has already been carried out and a speed of 100 terabits / s has been demonstrated," he said in an interview with the BBC. But for this, about 500 lasers had to be used, which in itself is very expensive.
Freude and colleagues have developed a technology for transmitting more than 300 subcarriers of different colors over an optical fiber with a single laser that operates in short pulses. This is where an interesting phenomenon called optical frequency comb comes into play. Each small pulse is "smeared" in frequency and time, so that the signal receiver, with good timing, can theoretically process each frequency separately.
After several years of work, German researchers still managed to find the right timing, select the right materials and put into practice the processing of each subcarrier using the Fast Fourier Transform (FFT). The Fourier transform is an operation that associates a function of a real variable with another function of a real variable. This new function describes the coefficients in the decomposition of the original function into elementary components - harmonic oscillations with different frequencies.
The FFT is ideal for splitting light into subcarriers. It turned out that about 350 colors (frequencies) can be extracted from a normal pulse in total, and each of them is used as a separate subcarrier, as in the traditional OFDM technique. Last year, Freude and his colleagues conducted an experiment and in practice showed a speed of 10.8 terabits / s, and now they have further improved the accuracy of frequency recognition.
According to Freude, the timing and FFT technology he developed could well be implemented in a microcircuit and find commercial application.
The speed of access over fiber optic lines is theoretically almost unlimited, but in practice the speed of the data transmission channel is 10 Mbps, 100 Mbps or 1 Gbps, this is the speed in the final section, that is, the speed with which the data actually arrives to the user and from him.
In 2012, the operation of a transatlantic underwater transmission channel of a new generation with a length of 6,000 kilometers began. Its bandwidth has reached 100 Gbps, which is much higher than the speed of satellite communications. Today, undersea fiber optic cables branch out right at the bottom of the ocean, providing the consumer with the highest speed Internet connection.
Scientists from the British Department of Defense have developed special glasses that allow soldiers to stay awake for 36 hours. Built-in optical microfibers project bright white light identical to the spectrum of sunlight around the retina of the eye, which "misleads" the brain.
The world's most high-speed communication line with a length of about 450 km was laid in France and connects Lyon and Paris. It is based on the technology of the "photon system" and allows data transfer at a record speed of 400 GB / s and a traffic volume of 17.6 terabits per second.
Scientists are working on technology to create fiber optic strands as thin as two nanometers. To do this, they use the web of the tiny spider Stegodyphuspacificus. The spider thread is dipped into a solution of orthosilicate tetraethyl, dried and fired at a temperature of 420°C. In this case, the web burns out, and the tube itself shrinks and becomes five times thinner.
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Most fiber technicians are aware of the difference between multimode and singlemode fibers. But not everyone is aware of the characteristics of optical fibers and the protocols for transmitting information through them. The article provides descriptions of specific characteristics of optical fibers and Ethernet transmission protocols, which sometimes cause conflicting interpretations.
Characteristics of optical fibers
There is probably no cable specialist working with optical fiber who would not know the difference between multimode fibers and single-mode fibers. We are not going to repeat common truths in this article. Let us dwell on the specific characteristics of optical fibers, which sometimes cause conflicting interpretations.
Optical fibers allow data signals to propagate along them, provided that the light signal is introduced into the fiber at an angle that provides total internal reflection at the interface between two media of two types of glass having different refractive indices. In the center of the core is extra pure glass with a refractive index of 1.5. The core diameter ranges from 8 to 62.5 µm. The glass surrounding the core, called the optical cladding, is slightly less free of impurities and has a refractive index of 1.45. The total diameter of the core and shell is in the range from 125 to 440 microns. Polymer coatings are applied over the optical cladding to reinforce the fiber, security threads, and outer cladding.
When optical radiation is introduced into the fiber, a beam of light incident on its end at an angle greater than the critical one will propagate along the interface between two media in the fiber. Every time radiation hits the interface between the core and cladding, it is reflected back into the fiber. The angle of input of optical radiation into the fiber is determined by the maximum allowable input angle, called numerical aperture or aperture fibers. If this angle is rotated along the axis of the core, a cone is formed. Any beam of optical radiation incident on the end of the fiber within this cone will be transmitted further down the fiber.
Being inside the core, optical radiation is repeatedly reflected from the interface between two transparent media having different refractive indices. If the physical dimensions of the optical fiber core are substantial, individual light rays will be injected into the fiber and subsequently reflected at different angles. Since the input of optical energy rays into the fiber was carried out at different angles, the distances they travel will also be different. As a result, they reach the receiving area of the fiber at different times. The pulsed optical signal that has passed through the fiber will be expanded compared to the one that was sent, therefore, the quality of the signal transmitted over the fiber will also deteriorate. This phenomenon has been named modal dispersion(DMD).
Another effect that also causes degradation of the transmitted signal is called chromatic dispersion. Chromatic dispersion is caused by the fact that light rays of different wavelengths propagate along the optical fiber at different speeds. When transmitting a series of light pulses through an optical fiber, modal and chromatic dispersion can eventually cause the series to merge into one long pulse, causing signal bit interference and loss of transmitted data.
Another typical characteristic of an optical fiber is damping. The glass used to make the optical fiber (OF) core is very pure, but still not perfect. As a result, light may be absorbed by the glass material in the optical fiber. Other optical signal losses in a fiber can be scatter and loss, as well as attenuation from poor optical connections. Splicing losses in fibers can be caused by misalignment of fiber cores or fiber end faces that have not been polished and cleaned properly.
Network Protocols for Optical Ethernet Transmission
Let's list the main Ethernet transmission protocols over multimode and single-mode optical fibers.
10BASE-FL- 10 Mbps Ethernet transmission over multimode fiber.
100BASE-SX- 100 Mbit/s Ethernet transmission over multimode optical fiber at a wavelength of 850-nm. The maximum transmission distance is up to 300 m. Longer transmission distances are possible using a single-mode optical fiber. Backwards compatible with 10BASE-FL.
100BASE-FX- 100 Mbit/s Ethernet transmission (Fast Ethernet) over multimode optical fiber at a wavelength of 1300-nm. The maximum transmission distance is up to 400 m for half duplex connections (with collision detection) or up to 2 km for full duplex connections. Longer distances are possible with the use of a single-mode optical fiber. Not backward compatible with 10BASE-FL protocol.
100BASE-BX- 100 Mbit/s Ethernet transmission over single mode fiber. Unlike the 100BASE-FX protocol, which uses two fibers, 100BASE-BX operates on a single fiber with WDM (Wavelength-Division Multiplexing) technology, which allows you to separate the signal wavelengths at reception and transmission. For transmission and reception, two possible wavelengths are used: 1310 and 1550 nm or 1310 and 1490 nm. Transmission distance up to 10, 20, or 40 km.
1000BASE-SX- 1 Gbit/s Ethernet transmission (Gigabit Ethernet) over multimode optical fiber at 850-nm wavelength and up to a maximum distance of 550 m, depending on the optical fiber class used.
1000BASE-LX- 1 Gbit/s Ethernet (GigabitEthernet) transmission over multimode optical fiber at a wavelength of 1300-nm for a maximum distance of up to 550 m. The protocol is optimized for transmission over long distances (up to 10 km) over single-mode optical fiber.
1000BASE-LH- - 1 Gbit/s Ethernet transmission over single-mode optical fiber for a maximum distance of up to 100 km.
10GBASE-SR- 10 Gbit/s Ethernet transmission (10 GigabitEthernet) over multimode optical fiber at a wavelength of over 850-nm. The transmission distance can be 26 m or 82 m, depending on the type of optical fiber used with a core of 50 or 62.5 microns. Support for transmission over a distance of 300 m via multimode optical fiber class OM3 and above, with a bandwidth ratio of at least 2000 MHz / km.
10GBASE-LX4- 10 Gbit/s Ethernet transmission over multimode optical fiber at 1300-nm wavelength. Uses WDM technology for transmission over distances up to 300m over multimode fibers. Support for transmission over single-mode fiber over distances up to 10 km.
In conclusion of the article, we present some data on the types of multimode optical fibers used and transmission standards. The data are summarized in Table 1 (excerpts from the Standards).
International Standard: ISO/IEC 11801 “GenericCablingforCustomerPremises”
International Standard: IEC 60793-2-10 “Product Specifications - Sectional Specification for Category A1 Multimode Fibers”
ANSI/TIA/EIA-492-AAAx “Detail Specification for Class 1a Graded-Index Multimode Optical Fibers”
(1) Class OM1 multimode optical fiber with 62.5-µm or 50-µm core.
(2) Class OM2 multimode optical fiber with 50-µm or 62.5-µm core.
(3) The OM4 class was ratified by IEEE in June 2010 and is the 802.ba Standard for 40G/100G Ethernet. Operates over distances up to 1000m over 1Gbps Ethernet, 550m over 10Gbps Ethernet, and 150m over 40Gbps and 100Gbps Ethernet network protocols.
(4) International Standard ISO/IEC 11801 defines the maximum attenuation value of OF. The IEC and TIA standards describe the (minimum) or average attenuation of a bare optical fiber.
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